In many applications, it is necessary to algorithmically quantify the similarity exhibited by two strings composed of symbols from a finite alphabet. Numerous string similarity measures have been proposed. Particularly well-known measures are based are edit distance and the length of the longest common subsequence. We develop a notion of n-gram similarity and distance. We show that edit distance and the length of the longest common subsequence are special cases of n-gram distance and similarity, respectively. We provide formal, recursive definitions of n-gram similarity and distance, together with efficient algorithms for computing them. We formulate a family of word similarity measures based on n-grams, and report the results of experiments that suggest that the new measures outperform their unigram equivalents.